JPH06120763A - Constant impedance voltage controlled variable attenuator - Google Patents

Abstract

PURPOSE:To provide the constant impedance voltage controlled variable attenuator where the extent of attenuation is not changed by temperature in all of a designated temperature range. CONSTITUTION:This device is so constituted that a received DC voltage is converted into a DC current and this current flows to a PIN diode 16 which is in series with respect to high frequency out of three PIN diodes 16-18 constituted into a pi type. Thus, the circuit characteristic is not changed by the change of temperature, and it is unnecessary to design the circuit again even if PIN diodes different in temperature characteristics are used, and readjustment is unnecessary regardless of the secular change of characteristics of PIN diodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant impedance voltage controlled variable attenuator having a voltage-current conversion circuit.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing the structure of a conventional constant impedance voltage controlled variable attenuator. In the figure, 1 is an input port for receiving a DC voltage, 2 and 5 are resistors, 7 is an operational amplifier for inverting and amplifying and adding a DC voltage to output a voltage,
Reference numeral 9 is a port for inputting a microwave signal, 10 is a voltage source of a variable attenuator, 11 is a resistor, 12 is a coil connecting the output of the operational amplifier 7 and the variable attenuator, 13, 14, 15, 2
0 is a capacitor, 16 is a high frequency series PIN diode, 17 and 18 is a high frequency parallel PIN diode, and a direct current is a PIN diode connected in series. 19 is a PIN diode 16 and a PIN diode 18 are grounded in a direct current. Resistor, 21 is a port for outputting a microwave signal, 3
Reference numerals 1 and 32 are thermistors that change their resistance values depending on temperature and adjust the output voltage of the operational amplifier 7.

Next, the operation will be described. When a DC voltage is received at port 1 in FIG.
And the resistance value of the thermistor 32, and the thermistors 31 and 3
Inversion amplification and addition are performed according to the ratio of the resistance values of 2 to output a voltage corresponding to the DC voltage received by the port 1. On the other hand, the microwave signal input from the port 9 in the constant impedance variable attenuator passes through the capacitor 13. When the output voltage of the operational amplifier 7 is 0V, no current flows in the PIN diode 16, so that the microwave signal passes through the PIN diode 17 in which the current flows and is grounded through the capacitor 15. Therefore, almost no microwave signal is output from the port 21. Operational amplifier 7
As the output voltage of the PIN diode 16 increases.
A current starts to flow in, and the microwave signal input from the port 9 passes through the PIN diode 16, and the amount of attenuation determines the amount of attenuation. Thermistor 3
1 and 32 change their own resistance values according to the temperature and change the output voltage of the operational amplifier 7 according to the temperature so that the amount of attenuation of the variable attenuator does not change with temperature.

[0004]

Since the conventional constant impedance voltage controlled variable attenuator is constructed as described above, the attenuation amount of the constant impedance voltage controlled variable attenuator at all temperatures within the specified temperature range. However, there is a problem that the temperature fluctuation cannot be eliminated. Also, P
If the temperature characteristics of the forward voltage and the forward current of the IN diode are different, there is a problem that the combination of the thermistors needs to be changed each time. Further, there is a problem that it is not possible to cope with the secular change in the temperature characteristic of the forward voltage vs. the forward current of the PIN diode.

The present invention has been made to solve the above problems, and it is an object of the present invention to obtain a constant impedance voltage control variable attenuator having no temperature fluctuation of the attenuation amount at all temperatures within a specified temperature range. The purpose is to obtain a constant impedance voltage control variable attenuator that does not require circuit modification even if PIN diodes having different temperature characteristics of forward voltage vs. forward current are used. It is an object of the present invention to obtain a constant impedance voltage control variable attenuator that does not require circuit modification even if the temperature characteristics of forward voltage vs. forward current change over time.

[0006]

A constant impedance voltage control variable attenuator according to the present invention converts a received DC voltage into a DC current, and converts the converted current into three π-type currents.
Among the IN diodes, it is configured to flow to a PIN diode serially connected in high frequency.

[0007]

The constant impedance voltage control variable attenuator according to the present invention converts the received DC voltage into a current and supplies it to the PIN diode. Therefore, even if the forward voltage vs. the forward current of the PIN diode varies with temperature, The current flowing through the PIN diode becomes constant with respect to the received DC voltage, and therefore the high frequency characteristics of the PIN diode also become constant, and as a result, there is no temperature variation in the attenuation amount of the constant impedance voltage control variable attenuator. For the same reason, even if there is an individual difference in forward voltage vs. forward current of the PIN diode, or if there is a secular change in temperature characteristics of forward voltage vs. forward current,
There is no temperature fluctuation of the attenuation amount of the constant impedance voltage control variable attenuator.

[0008]

Embodiment 1 FIG. 1 shows the configuration of a constant impedance voltage control variable attenuator according to Embodiment 1 of the present invention. In FIG. 1, reference numerals 1, 2, 5, 7, 10 to 21 are the same as the conventional ones. Reference numerals 3 and 6 are resistors, 4 is a reference resistor, and 8 is an operational amplifier for a voltage follower.

Next, the operation will be described. In FIG. 1, the DC voltage received at the port 1 is inverted and amplified by the operational amplifier 7, and a voltage is applied to the reference resistor 4. Therefore, the reference resistance 4
An electric current flows through. When the current flowing through the reference resistor 4 increases for some reason, a voltage lower than the voltage value output from the operational amplifier 7 is applied to the operational amplifier 8. Operational amplifier 8
Since they constitute a voltage follower, the input and output voltages of the operational amplifier 8 are equal. Therefore, the potential of the + side terminal of the operational amplifier 7 decreases. As a result, a potential difference is generated between the +/− terminals of the operational amplifier 7, and the output voltage of the operational amplifier 7 tries to decrease,
It works so that no current flows through the reference resistor 4. At this time, a high voltage is applied to the operational amplifier 8 and the output voltage also increases.
In this way, when a current flows in the reference resistor 4, it acts so that it does not flow, and when it does not flow, it acts so that it does not flow. Flowing.

Next, it is shown that the PIN diode 16 of the constant impedance voltage control variable attenuator, which is serially connected in high frequency, has a great influence on the amount of attenuation for the microwave signal. If we consider the PIN diode as a variable linear resistance,
The PIN diode configured in the mold can be regarded as equivalent to that shown in FIG. The attenuation amount of the microwave signal at this time can be expressed by the following formula.

[0011]

[Equation 1]

If R ₃₃ , R ₃₄ , and R ₃₅ are respectively 178.49Ω, 30.40Ω, and 50Ω in the equation 1, the attenuation amount A is about −5 dB. Next, R ₃₃ is set to 160.641Ω which is 10% smaller than that, and if the attenuation A is calculated without changing R ₃₄ and R _{35, it} is about −5.09 dB from “Equation 1”.
Becomes Similarly, R _{34 is set} to 27.36Ω, and R ₃₃ and R ₃₅
If the attenuation A is calculated without changing,
It becomes 4.6 dB. From the above calculation results, the change in the resistance value of R ₃₄ has a greater effect on the attenuation amount than the change in the resistance value of R ₃₃ .

From the above, the constant impedance voltage control variable attenuator shown in FIG.
Since the amount of current flowing through the diode is set to a value corresponding to the received DC voltage regardless of the temperature, the attenuation amount of the microwave signal does not change even if the temperature changes.

Embodiment 2 FIG. 2 shows the configuration of a constant impedance voltage controlled variable attenuator according to Embodiment 2 of the present invention. 1 in the figure
21 are the same as those in the first embodiment. 28, 29, 3
0 is a PIN connected in a π-type like 16, 17, and 18
Diodes, 25 and 26 are capacitors, 24 is a first-stage PIN diode 16 and a second-stage PIN diode 28
Is a coil connecting DC in series, 27 is a capacitor grounding between the PIN diode 23 and the PIN diode 24, 22 is a voltage source of the second-stage variable attenuator,
Reference numeral 23 is a resistance.

Next, the operation will be described. In the second embodiment, the parts 9 to 18 of the variable attenuator of the first embodiment are connected in two stages in series. 9 to 21 are the same operations as those in the first embodiment. A current having the same value as that of the PIN diode 16 always flows through the PIN diode 28 which is connected in series with the PIN diode 16 in terms of high frequency and direct current.
Therefore, the first-stage variable attenuator and the second-stage variable attenuator can always have the same attenuation amount for the microwave signal.

[0016]

Since the present invention is configured as described above, the high frequency serial PIN diode of the constant impedance variable attenuation circuit section is supplied with a current having a value corresponding to the received DC voltage regardless of temperature. Since it flows, the amount of attenuation with respect to the microwave signal does not change with temperature. Further, even when a PIN diode having different temperature characteristics of forward voltage vs. forward current is used, a constant current corresponding to a direct current voltage flows through the PIN diode, so there is no need to change the design. Further, even if the temperature characteristic of the forward voltage versus the forward current of the PIN diode changes over time, it is not necessary to readjust the circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a constant impedance voltage control variable attenuator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a constant impedance voltage control variable attenuator according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional constant impedance voltage controlled variable attenuator.

FIG. 4 is a diagram showing a π-type attenuator.

[Explanation of symbols]

 1 DC voltage input port 2 Resistance 3 Resistance 4 Reference resistance 5 Resistance 6 Resistance 7 Operational amplifier 8 Operational amplifier 9 Microwave signal input port 10 Power supply 11 Resistance 12 Coil 13 Capacitor 14 Capacitor 15 Capacitor 16 PIN diode 17 PIN diode 18 PIN diode 19 Resistor 20 Capacitor 21 Microwave signal output port 22 Power supply 23 Resistor 24 Coil 25 Capacitor 26 Capacitor 27 Capacitor 28 PIN diode 29 PIN diode 30 PIN diode 31 Thermistor 32 Thermistor 33 Resistor 34 Resistor 35 Resistor

Claims (2)

[Claims] 1. A constant impedance voltage control variable attenuator having a characteristic that an attenuation amount for a microwave signal becomes a value corresponding to the DC voltage when receiving the DC voltage, and the received DC voltage is an operational amplifier. A voltage-current conversion circuit for converting into a direct current by using, and three PIN diodes are connected in a π-type, two PIN diodes parallel in high frequency are connected in series in terms of direct current, and one in high frequency is connected in series. P
The IN diode and the two PIN diodes parallel in high frequency have a constant impedance variable attenuation circuit configured to be grounded via the same resistance in terms of direct current,
A constant impedance voltage control variable attenuator, characterized in that an output current of the voltage-current conversion circuit is configured to flow through a high frequency series PIN diode of the constant impedance variable attenuation circuit. 2. A constant impedance voltage control variable attenuator having a characteristic that the amount of attenuation for a microwave signal when receiving a DC voltage becomes a value corresponding to the DC voltage, and the received DC voltage is an operational amplifier. A voltage-current conversion circuit for converting into a direct current by using, and three PIN diodes are connected in a π-type, two PIN diodes parallel in high frequency are connected in series in terms of direct current, and one in high frequency is connected in series. P
The IN diode and the previous two PIN diodes have a plurality of constant impedance variable attenuation circuits configured to be grounded via the same DC resistance, and the output current of the voltage-current conversion circuit is A constant impedance voltage controlled variable attenuator, characterized in that it is configured so as to flow equally through all the high frequency serial PIN diodes of a plurality of constant impedance variable attenuator circuits.